In a multi-node communication network, synchronization may be employed to coordinate transmissions amongst the nodes. Synchronization may be implemented with respect to carrier frequencies, symbol or sample timing rates, and time stamp clocks.
Nodes within a multi-node communication network may be configured to comply with one or more synchronization standards. For example, a Multimedia Over Coaxial Cable Alliance (MoCA), (http://www.mocalliance.org), develops standards for networking over coaxial cable. Existing MoCA standards include MoCA 1.0 and MoCA 1.1, released together referred to herein as MoCA 1.X. A MoCA 2.0 standard is currently under development.
A multi-node communication network may include a management node and one or more client nodes. In a MoCA environment, management nodes are referred to network coordinators (NCs), and client nodes are referred to as existing nodes (ENs). For illustrative purposes, this terminology is used herein.
A NC may utilize a time stamp clock to schedule events and communication bandwidth amongst ENs. The ENs may maintain corresponding time stamp clocks to perform in accordance with scheduled events.
The NC may send a time stamp, or current count of the network coordinator time stamp clock, to an EN to synchronize the current count of the EN time stamp clock to the current count of the NC time stamp clock.
The NC time stamp clock and the EN time stamp clock are each driven by corresponding clock signals or counting rates. Where a counting rate of the EN time stamp clock is not synchronized to a counting rate of the NC time stamp clock, the current count of the EN time stamp clock may drift from the current count of the NC time stamp clock.
MoCA 1.X and MoCA 2.0 include specifications for a NC to provide a current count or time stamp to an EN. Time stamps may be provided to an EN when the EN initially connects to the network. Subsequent time stamps may be provided in beacons sent from the NC to schedule events or communication bandwidth.
In order to increase capabilities within a network and provide more efficient use of communication bandwidth, MoCA 2.0 adds new synchronization specifications and reduces tolerances of some existing synchronization specifications. For example, under MoCA 2.0, multiple ENs concurrently transmit reservation requests to a NC in an OFDMA mode. Multiple ENs may simultaneously transmit physical layer or PHY-frames, with each EN utilizing a corresponding NC-assigned subset of sub-carriers. The OFDMA PHY-frames may include reservation requests and/or other information directed to the NC, effectively providing a multipoint-to-point transmission. The NC may receive what appears as a single PHY-frame, a payload of which may be de-multiplexed for recovery. To maintain orthogonality of the combination of sub-carriers transmitted from multiple ENs, EN OFDMA transmitters are to synchronize corresponding sub-carriers to corresponding sub-carriers of the NC, adjust corresponding transmissions to arrive simultaneously at the NC, and adjust amplitudes of the corresponding transmissions as specified by the NC.
Under MoCA 1.X, an EN is to synchronize a local time stamp count to the NC time stamp count within 2.2 micro seconds (μs).
Under MoCA 2.0, an EN is to synchronize the local time stamp count to the NC time stamp count within 0.1 μs, with a counting rate accuracy of +/−20 parts per million (ppm). MoCA 2.0 provides a ranging mechanism to determine a time delay between an EN and a NC, and to use the time delay to provide a more accurate time stamp to the EN.
Under MoCA 1.X, an EN transmitter is to maintain a carrier frequency within +/−100 ppm of the NC carrier frequency.
Under MoCA 2.0, an EN is to synchronize a transmit carrier frequency to within +/−1 kHz of the NC carrier frequency. For a carrier frequency of approximately 1.5 GHz, this correlates to approximately 0.7 ppm.
Under one proposed MoCA 2.0 specification, for any given node, a transmitter symbol clock and a transmitter carrier frequency are to be derived from a common reference frequency.
Under the aforementioned MoCA 2.0 specification, a counting rate of a NC time stamp clock, and a frequency of a NC transmit carrier signal, are to be derived from a common reference frequency.
In the drawings, the leftmost digit(s) of a reference number identifies the drawing in which the reference number first appears.